1. Field of the Invention
The invention relates to a cold gas generator for an airbag system comprising a storage device filled with a gas under pressure; a gas outlet opening which in the rest state is pressure-tightly closed by a thin-walled sealing disk; a support device for supporting the sealing disk against the gas pressure acting on it; and a triggering device for affecting the support device, wherein the support device comprises a pressure plate resting against the sealing disk and a support lever supporting the pressure plate as well as the sealing disk.
2. Description of the Related Art
Known cold gas generators have a storage device in which the gas is stored at ambient temperature under high pressure for filling an airbag, when needed. In the rest state, a gas outlet opening is closed in a gas-tight way so that the gas pressure is maintained over the service life of the cold gas generator. A control device which is activated in case of an accident produces a signal which actuates the triggering device for opening the gas outlet opening. The gas stored in the storage device can then flow through the gas outlet opening and a correlated supply path into the folded airbag. The airbag is inflated whereby the gas expands to the desired filling pressure because of the correlated volume increase. The desire for a light-weight construction in the automobile industry as well as for improved safety measures with optionally a plurality of airbags and cold gas generators has resulted in the demand that they be constructed smaller and lighter, and have a more reliable function. The small size results in a high storage pressure of the gas in the storage device which leads to complex requirements in particular in the area of the gas outlet opening and the triggering device. On the one hand, the closure of the gas outlet opening must be configured such that it withstands high gas pressure while sealing it permanently gas-tightly even with respect to diffusion processes. Moreover, the triggering mechanism must be configured such that an accidental erroneous triggering is prevented and a controlled triggering with an energy expenditure as little as possible can take place.
In this connection, different configurations are known from German patent application 195 40 61 8 A1 in which the gas outlet opening is closed by a gas-tight film. The gas tight film is sized such that by itself it cannot withstand the pressure force of the filled-in gas. In the rest state, a support device supports the sealing film against the gas pressure acting on it. The support device has a pressure plate resting against the sealing film and also comprises a support element. The pyrotechnical charge acts, when needed, onto the support device such that its support action is eliminated. The gas pressure then destroys the sealing film so that the stored gas can be released in order to fill an airbag.
In the aforementioned prior art reference different configurations of the support device are illustrated in which the support device is a unitary part and is plastically deformed by the pyrotechnical charge such that its support action is eliminated. For supporting the sealing film against high gas pressure the support device must be sized to be correspondingly strong. This has the result that for its plastic deformation a large amount of energy must be provided by the pyrotechnical charge.
In one variant the pressure plate is supported by an elbow lever whose elbow joint is angled and is supported against the pyrotechnical charge. In the triggering situation, the pyrotechnical charge must first stretch the elbow joint against the gas pressure acting on it which requires a high energy expenditure. The permanent support of the elbow joint on the pyrotechnical charge prevents maintenance and inspection work. Minimal mounting tolerances can result in an accidental tearing of the sealing film.
In a further variant, the support plate is configured as a unitary part of the support element. For opening the gas outlet opening, the pyrotechnical charge acts laterally on it wherein the support device carries out a pivot movement. When carrying out this pivot movement, the edge of the pressure plate facing the triggering device must be lifted against the sealing film and the gas pressure acting on it before triggering can occur. This also requires a correspondingly high energy expenditure. The illustrated embodiments are sensitive with regard to tolerances in the area of the support and of the triggering device. Minimal movements can result in an accidental tearing of the sealing film.
It is an object of the present invention to provide a cold gas generator with improved reliability and reduced actuation energy.
In accordance with the present invention, this is achieved in that the pressure plate and the support lever are configured separately from one another, in that the support lever is supported in a pivotable way on a bearing so as to receive forces in the pressure direction and to be force-free in a direction transverse thereto, and in that the triggering device acts on the support lever so as to pivot it about the bearing.
It is thus suggested to close the gas outlet opening with a sealing disk in a pressure-tight way and to support the sealing disk in the rest state on a support device which is comprised of a pressure plate resting against the sealing disk and a separately configured support lever. The support lever is supported on the bearing so as to be pivotable and receive forces in the pressure direction while being force-free in a direction transverse thereto. The corresponding triggering mechanism is configured such that in the release situation the support lever pivots about its bearing. With this configuration, the triggering device in the rest state is not loaded by the support device. Mounting tolerances of the triggering device have no effect on the support action of the support device. With the above described bearing and the type of actuation of the support lever, its actuation does not result in a lifting of the pressure plate or of the sealing disk counter to the gas pressure acting thereon. For the actuation to take place, only a minimal energy level for overcoming the occurring frictional forces is required. As a result, the triggering device can be small which, in addition to weight and space savings, also results in a reduction of the released amount of pollutants, particularly in the case of employing a pyrotechnical charge.
The pivotable end of the support lever has advantageously a rounded portion whose radius matches in particular approximately the spacing of the pivotable end from the bearing. In this way, the support lever can carry out a certain pivot stroke which leaves the support action unchanged. This enables generous positional tolerances for the support lever without impairing its support action; this contributes to the prevention of accidental erroneous triggering. Advantageously, a corresponding rounded recess is provided on the pressure plate and is engaged by the rounded pivotable end of the support lever. This provides a safe guiding and mutual adjustment.
A static gas pressure acts on a closed opening perpendicularly to its opening plane. A center axis of the opening extending perpendicularly to the opening plane and positioned at the center of gravity of the surface area of the opening therefore also defines the position and alignment of the resultant pressure force. By arranging the bearing on the center axis of the opening of the gas outlet opening, the resultant pressure force is oriented toward the bearing so that unsymmetrical loading of the support device is prevented; this contributes to a reduction of the triggering energy. Another contribution to the reduction of triggering energy is made by the configuration of the bearing of the support lever as a shaft journal by which the resultant frictional forces and, as a result of this, the required actuation energy can be kept minimal.
In an expedient configuration the pressure plate is fitted into the gas outlet opening approximately without play in the radial direction relative to the opening axis. In this way, a play-enabled movability of the pressure plate in the radial direction and the risk of damaging the sensitive sealing disk correlated therewith are avoided. Advantageously, the gas outlet opening and the pressure plate have approximately axis-parallel peripheral walls so that the pressure plate is guided about a defined axial stroke while avoiding tilting. This contributes to a precisely defined triggering process. By avoiding a tilting movement, certain axial position tolerances of the pressure plate are also permissible in the rest state without the risk of an accidental bursting of the sealing disk. Moreover, the pressure plate with its comparatively great thickness and gap-free fitting provides a certain sealing action.
In particular for an areal connection of the pressure plate with the sealing disk leakage by gas diffusion is prevented because the sealing disk is configured with a thin wall so as to extend only linearly along the peripheral wall of the pressure plate. The area of the thin-walled configuration of the sealing disk with a correspondingly high gas diffusion rate is thus very small. Moreover, with this configuration a precisely defined line-shaped breakage point results in the sealing disk wherein, in the case of triggering, the pressure plate with the correlated connected sealing disk part is ejected. As result of this, the now open gas outlet opening a has a precisely defined geometry with correspondingly predeterminable flow properties. In this way, the cold gas generator and the airbag to be filled can be adjusted relative to one another with greater precision with regard to their construction; this contributes to the operational safety of the system.
For a precise matching of the flow behavior, a flow throttle is provided in the flow path of the gas, in particular, at the storage device side of the gas outlet opening. In this arrangement, in the rest state the complete static pressure acts on the gas outlet opening which enables a precise tearing or bursting of the sealing disk. After opening of the gas outlet opening, a flow process takes place according to which a reduced dynamic gas pressure through the flow throttle results.
In particular, in connection with helium as a gas in the storage device a series of advantages can be obtained. Helium has excellent flow properties which enable a connection of an airbag by a supply line of a corresponding length to the storage device. In this way, positioning of the storage device at a location remote from the airbag is possible which improves the mounting flexibility of the airbag system. As a result of the minimal dependency of helium on pressure and temperature, the filling pressure of the storage device can be selected such that, on the one hand, a safe filling of the airbag is possible at low ambient temperatures and, on the other hand, for example, in the case of intensive solar radiation, the gas pressure will not increase excessively so that an overloading of the airbag at high temperatures is prevented. Moreover, an airbag filled with helium has excellent damping properties so that the impact loading of a person to be protected and, in particular, the HIC factor (Head Injury Criterion) is reduced. The flow throttle prevents also a sudden inflation of the airbag and thus a possible overloading of the airbag material.
In an advantageous embodiment, a housing, particularly of a unitary (single part) construction is provided in which the gas outlet opening, the support device, and optionally also the flow throttle are arranged. The housing is expediently welded gas-tightly to the storage device. In this way, a precise alignment and support of the individual parts relative to one another is enabled by means of an excellently controllable manufacturing process. The unitary configuration of the housing also prevents possible displacement events as a result of high forces that are occurring. The housing, for example, can be welded in a cost-saving way onto the storage device only after a pre-mounting step.
Advantageously, the support lever has a pawl lever angled relative to the axis of the opening wherein the triggering device is displaced axis-parallel and laterally to the axis of the opening or bearing for acting on the pawl lever. By means of the pawl lever a deflection device is provided that for actuation of the pivotable end transverse to the pressure direction has an actuation direction parallel to the central axis of the opening. In this way, the triggering device can be arranged parallel to the axis of the opening so that over all an elongate narrow configuration of the cold gas generator is possible. This contributes to universal placement possibilities of the corresponding cold gas generator even in tight spaces in the vehicle. The slender configuration is further enhanced by a triggering mechanism having a longitudinally guided impact piston.
In contrast to pivoting or rotating systems, a slender configuration is also enabled as a result of the longitudinally displaceability of the piston. The impact piston is secured preferably in the receptacle by a clamping ring. The clamping ring acts as a mounting aid and secures the impact piston in its rest position without a support action being required by the support lever.
For generating a high energy density and, correlated therewith, minimal space and weight requirements for actuation of the impact piston a pyrotechnical charge is provided. The pyrotechnical charge is secured together with the impact piston in the receptacle and secured by a securing ring against sliding out. The securing ring is expediently elastically embodied so that in the case of ignition of the charge it can act as a seal. For an additional reduction of the space the impact piston comprises an interior piston chamber which is enclosed partially by a piston jacket and a piston bottom. The pyrotechnical charge projects into this piston chamber so that overall a compact configuration results.
The impact piston and the pawl lever can expediently be provided with a contact surface, respectively, angled in the rest state relative to one another. Upon impacting of the impact piston onto the slanted contact surface of the pawl lever, the pawl lever performs a pivot movement to such an extent that the two impact surfaces will reach a position in which they are in a plane adjacent to one another. In this state, the rotational movement of the pawl lever is braked so that it remains in a defined position without negatively affecting the outflow of the gas. In a further expedient configuration, the impact piston has a curved contact surface which in connection with the pivoting pawl lever can roll on it. In this way, overall the frictional losses are reduced which results in a further saving in regard to the energy requirements and thus also in a reduction of the size of the triggering device. In this connection it may be expedient to configure the contact surface of the impact piston smaller than the piston surface. By means of the relatively large piston surface a high piston force can be achieved. The comparatively smaller contact surface can even enable an improved movability of the support lever or of the pawl lever in the case of corresponding spatial conditions.